THE WEB OF LIFE 359 



That the web of inter-relations includes human interests 

 may be illustrated by reference to the role of birds in 

 preserving the balance of Nature. All other life depends on 

 plant life ; but the great check on plant hfe is that of 

 insect hfe — overwhelming in numbers, overmastering in 

 devices, and appalhng in voracity ; and the great check 

 on insect Hfe is bird hfe — and, luckily for tis,tliis again is 

 abundant, alert, and well appetized. It is very interesting 

 that the two great classes of successful fliers should be 

 thus, in the wide economics of Nature, pitted against one 

 another, wings against wiags, freeman against freeman. 

 Invertebrate against Vertebrate, ' httle brain ' against 

 ' big brain,' ' instinct ' against ' intelhgence.' Practically 

 this is the most important conflict of classes that the 

 world knows. 



There is a biological suggestiveness in the old saying 

 about the dead flies which spoil the ointment of the apothe- 

 cary, but it was not till quite recently that the important 

 role of flies as disease- disseminators was discovered. 

 Perhaps it was at the time of the Spanish-American war 

 that it began to be clearly recognized that the house-fly 

 was a carrier of enteric fever and therefore full of menace. 

 It is now generally recognized that the house-fly can scatter 

 the germs not only of enteric, but of typhoid fever and of 

 cholera, and perhaps of other diseases as well, such as 

 infantile diarrhcea. It is also known to carry the tubercle 

 bacillus. Wherever there is a breeding ground, e.g. 

 about a heap of stable manure, and the possibihty of 

 contamination with disease-germs, the house-fly becomes 

 a most serious danger as a disseminator. What is true for 

 Britain is not less true for the United States, as Dr. L. 0. 

 Howard has proved up to the hilt. 



